1. Field of the Invention
The present invention is directed to producing CO2-depleted hydrocarbons from CO2-rich hydrocarbon resources. In particular, the present invention is directed to underwater scrubbing of CO2-containing hydrocarbon resources with an aqueous stream to produce a CO2-depleted hydrocarbon resource and a CO2-enriched aqueous stream.
2. Description of the Related Art
CO2 is a well known environmental pollutant that contributes to atmospheric warming via the Greenhouse effect. CO2 is a common contaminant in hydrocarbon resources such as, for example, natural gas. Generally, only a minimal amount, typically less than about 10 mole %, preferably less than about 5 mole %, of CO2 can be tolerated in a natural gas feed to a synthesis gas generating process. Unfortunately, in instances where CO2-rich hydrocarbon resources have CO2 levels higher than about 10 mole %, no economic method exists for removing the CO2 from the hydrocarbon resources. In addition, when the CO2 is removed, disposal of the CO2 is problematic.
Efforts have been made to dispose of CO2 by injecting it as a compressed gas into underground reservoirs. Also, studies have been done to determine whether CO2 can be disposed of in deep marine environments. However, in existing CO2 disposal methods, CO2 is obtained in a relatively pure state by compressing it and/or condensing it. Thus, a disadvantage of such disposal techniques is that they require costly compressors and/or refrigerators to compress and/or condense CO2.
For example, U.S. Pat. No. 6,190,301, to Murray, describes a process and vehicle for disposal of CO2. In Murray, gaseous CO2 is first solidified and allowed to free fall in a marine environment through open water where it at least partially embeds itself into sedimentary formations. Sedimentation of the CO2 ensures that the marine environment serves as a carbon sink through carbonate sequestration. Accordingly, Murray describes converting gaseous CO2 into a solid, requiring the use of expensive refrigeration and compression processes.
Also, U.S. Pat. No. 6,170,264 to Viteri, describes a low or no pollution engine for delivering power to vehicles or for other power applications. In the engine of Viteri, fuel and oxygen are combusted within a gas generator, generating water and CO2 with carbon-containing fuels. The combustion products, steam, carbon-containing fuels and CO2 are then passed through a condenser where the steam is condensed and the CO2 is collected or discharged. The CO2 is compressed and cooled so that it is in a liquid phase or super critical state. The dense phase CO2 is then further pressurized to a pressure matching a pressure, less hydrostatic head, existing deep within a porous geological formation, a deep aquifer, a deep ocean location or a terrestrial formation from which return of the CO2 into the atmosphere is inhibited. Accordingly, Viteri describes disposing of CO2 from a power generation plant into the ocean or a terrestrial formation, wherein CO2 gas is first compressed and cooled to form a liquid phase which is then further compressed to match the hydrostatic head.
As a result, there is an urgent need for a process and apparatus that can economically remove CO2 from hydrocarbon resources, without having to employ costly compression and/or condensation processes, and that can dispose of the removed CO2 in a manner that isolates the CO2 from the environment.
The present invention satisfies the above objectives by providing a process that not only economically removes CO2 from hydrocarbon resources, but also disposes of the removed CO2 in a manner that isolates the CO2 from the environment.
The process of the present invention removes CO2 from hydrocarbon resources by contacting a hydrocarbon resource with an aqueous stream, preferably at an elevated pressure. More specifically, processes of the present invention separate CO2 from a hydrocarbon resource by scrubbing the resource with an aqueous stream at elevated pressure, producing a CO2-containing aqueous stream that can be disposed of, for example, in at least one of a marine environment, a terrestrial formation or combination thereof. Thus, one important advantage of the present invention is that it can remove CO2 from hydrocarbon resources without having to use costly compression and/or condensation processes. An additional advantage, is that the present invention can dispose of removed CO2 in an aqueous stream in, for example, a marine environment, a terrestrial formation or combination thereof, thereby effectively isolating the CO2 from the environment.
In particular, a process, according to the present invention, for removing CO2 from a CO2-containing hydrocarbon asset can include contacting the hydrocarbon asset with an aqueous stream at an underwater location so that at least a portion of the CO2 in the hydrocarbon asset is dissolved into the aqueous stream, creating a CO2-depleted hydrocarbon asset and a CO2-enriched aqueous stream. The CO2-enriched aqueous stream is then separated from the hydrocarbon asset. Finally the CO2-enriched aqueous stream is disposed of in at least one of a marine environment, a terrestrial formation or combination thereof.
In addition, a method, according to the present invention, for producing a CO2-depleted hydrocarbon gas from a hydrocarbon/CO2 gas mixture can include contacting a hydrocarbon/CO2 gas mixture underwater with an aqueous stream, so that at least a portion of the CO2 in the gas mixture is dissolved into the aqueous stream, creating a CO2-depleted hydrocarbon gas and a CO2-enriched aqueous stream. Next, the CO2-enriched aqueous stream is separated from the gas stream. Finally, a CO2-depleted hydrocarbon gas is produced.